FIGS. 9 and 10 are views illustrating conventional press apparatus for a common paper machine. FIG. 9 is a schematic view showing a configuration of a no-open draw type press of the press apparatus, and FIG. 10 is a schematic view showing a configuration of an open draw type press of the press apparatus.
It is to be noted that the no-open draw type press is a press configuration wherein a wet web 1 travels in a press section 2 of a paper machine in a state wherein the both faces or one face of the wet web 1 is always retained by a felt, a belt or the like as shown in FIG. 9. Meanwhile, the open draw type press is a press configuration wherein a wet web 1 travels in a press section 2 of the paper machine in a state wherein none of the both faces of the wet web 1 is always retained by a felt, a belt or the like as shown in FIG. 10.
As shown in FIG. 9, in a common no-open draw type press, a wet web 1 fed through a press or a former on the upstream side of a final water-removing press 4 of the paper machine is sucked by a suction roll 5a and retained on a felt 6a. Thereafter, the wet web 1 is transported in a state wherein it is sandwiched by the felt 6a and another felt 6b to the final water-removing press 4.
In the present example, the final water-removing press 4 includes a press roll (or shoe press) 4a and another press roll 4b, and utilizes a nip pressure of the press rolls 4a and 4b to transfer water content included in the wet web 1 to the felts 6a and 6b to perform water removal.
The wet web 1 dewatered by the final water-removing press 4 travels while it is sucked by a suction roll 5b and supported by the felt 6b until it is sucked by a suction roll 5c and supported by a canvas 7a and then carried to a dryer section 3. It is to be noted that, where a paper feeding (threading) belt which does not have air permeability and absorbs no water content at all is provided in place of the felt 6b, the suction roll 5b need not be provided.
Thereafter, the wet web 1 passes a first dryer 3a, a second dryer 3b and a third dryer 3c of the dryer section 3 in order, whereupon drying of the wet web 1 is performed. It is to be noted that reference character 7a in FIG. 9 denotes a canvas, and reference characters 20a and 20b in FIG. 9 denote each a vacuum roll.
Such a no-open draw type press as described above is disclosed, for example, in U.S. Pat. No. 5,611,892 (hereinafter referred to as Patent Document 1) and Japanese Published Examined Application No. HEI 3-45156 (U.S. Pat. No. 4,493,351: hereinafter referred to as Patent Document 2). Also in the techniques disclosed in Patent Documents 1 and 2, water removal is performed by a press section in a state wherein a wet web is retained by a felt or a belt (that is, no-open draw), and thereafter, the wet web is carried to a dryer section 3.
Meanwhile, as shown in FIG. 10, in a common open draw type press, a wet web 1 is dewatered by a nip section of press rolls 9a and 9b in a state wherein the wet web 1 is sandwiched by felts 6c and 6d. Thereafter, the wet web 1 is dewatered by a nip section of a press roll (center roll) 9c and another press roll 9d in a state wherein one face of the wet web 1 is retained by the felt 6c. Then, the wet web 1 is dewatered by a nip section of the press roll 9c and a further press roll (or shoe press) 9e in a state wherein the one face of the wet web 1 is supported by a felt 6e. 
Thereafter, the wet web 1 is sucked by open draw by a suction roll 5d through a paper roll 18 and is then dewatered by a nip section of a press roll 4c and another press roll (or shoe press) 4d of the final water-removing press 4 in a state wherein one face of the wet web 1 is retained by a felt 6f. Thereafter, the wet web 1 is carried by open draw to a smoothing press 10 through the paper roll 8.
The smoothing press 10 is provided on the downstream side of the final water-removing press 4, and includes a press roll 10a having a soft cover (for example, a rubber skin) mounted on the surface thereof and a press roll 10b having a hard cover (skin harder than the soft cover) mounted on the surface thereof.
The smoothing press 10 generates a nip pressure lower than that of a normal press. Further, if the surface of one of the press rolls thereof is formed as a soft surface [approximately 85° to 95° in the type A of the JIS Standards (JIS K 6253)], then a nip width can be secured, and the smoothness of the surface of the wet web 1 can be enhanced in a state wherein the quantity (thickness or volume) of the wet web 1 is retained in the nip section of the smoothing press 10.
Such an open draw type press as described above is disclosed, for example, in a catalog [Mitsubishi-Beloit Press] (September 1980: hereinafter referred to as Non-Patent Document 1). Also in the technique of Non-Patent Document 1, a smoothing press is provided on the downstream side of a final water-removing press, and a wet web on the upstream side and the downstream side of the smoothing press is carried by open draw.
Incidentally, as described above, in the no-open draw type press, since the wet web 1 is retained by felts or belts, the wet web 1 can be fed with stability also upon high-speed operation. Further, damage to the wet web 1 can be prevented, and a paper feeding performance is enhanced.
However, in such a no-open draw type press as described above, there is the possibility that the smoothness of the surface of the wet web 1 which contacts with the felts 6a and 6b may be degraded.
Particularly recently, there is a tendency that the number of press apparatus in a press division is decreased. However, if the number of press apparatus is decreased, then the number of nip sections decreases, and as a result, the water removal efficiency in the press division drops. Therefore, while it is a possible idea to use a felt whose surface has fibers of an increased fiber diameter (butt diameter) to enhance the drainability, the smoothness of the surface of the wet web 1 is degraded still more. In particular, in a normal multi-stage type press, a felt whose surface layer has fibers of an increased fiber diameter (butt diameter) (14 to 18 d) is used for a press at the preceding stage attaching importance to the drainability while a felt whose surface has fibers of a smaller fiber diameter (butt diameter) (6 to 10 d) is used for a press at the succeeding stage attaching importance to the surface characteristic. However, also in such a configuration as described above, there is a tendency that the smoothness of paper on the felt side is lower (coarser) than that on the roll side. Particularly, where the number of press stages is decreased, functions of the drainability and the smoothness which are contrary to each other are required to the felt, and satisfaction of the functions only by the countermeasure on the felt side is difficult.
Therefore, in order to enhance the smoothness of the wet web 1 in the no-open draw type press, it is a possible idea to provide the smoothing press 10 described above on the downstream side of the final water-removing press 4. However, since the conventional smoothing press 10 is configured originally so that it can be applied only to an open draw type press, it is difficult to incorporate the smoothing press 10 as it is in the no-open draw type press.
Meanwhile, in the open draw type press described above, since the smoothing press 10 is provided, the smoothness of the wet web 1 can be enhanced. However, as shown in FIG. 11, if high-speed operation is performed, then apparatus vibration generally increases. Consequently, there is a subject that, since the surface of the soft cover press roll 10a of the smoothing press 10 is corrugated by the increased apparatus vibration and gives rise to generation of further violent vibration, the high-speed operation is difficult.
Further, in the open draw type press, an open draw portion of the wet web 1 is long on the upstream side and the downstream side of the smoothing press 10. Therefore, where high-speed operation is performed, the wet web 1 is likely to break at the open draw portion, and enhancement of the paper feeding performance is difficult.
In this manner, the conventional no-open draw type press and open draw type press individually have advantages and disadvantages, and particularly where it is tried to operate a paper machine at a higher speed, it is difficult to enhance the smoothness of the wet web 1 while the wet web 1 is carried with stability.
The present invention has been made in view of such subjects as described above, and it is an object of the present invention to provide a smoothing press for a paper machine and a press for a paper machine with a smoothing press as well as a paper production method which can enhance the paper feeding performance and the smoothness of a wet web also upon high-speed operation of a paper machine.